This invention relates to a material having a plurality of profile co-extruded layers and a profile co-extrusion system for making the same.
Dynamo-electric machines such as power generators include a rotor mounted within a stator. The rotor is an electromagnet that includes field coils typically made of copper or aluminum. A body of the rotor, typically made of steel, includes multiple axial slots. The field coils are arranged within these axial slots and produce a magnetic flux pattern when supplied with electrical current. A turbine (e.g., a gas or steam turbine) rotates the rotor including the field coils so that the magnetic flux pattern interacts with windings of the stator to generate electrical power.
The field coils must be electrically and mechanically isolated from the rotor body via rotor slot insulation. This insulation is designed to withstand the electrical, mechanical and thermal forces induced during normal operation of the dynamo-electric machine for twenty years or more. The rotor slot insulation often includes the following multiple parts:slot armor and a sub-slot cover. These parts serve to position and protect the field coils from electrical contact with the rotor body. Specifically, the slot armor insulates the coil's sides. The slot armor also provides electrical creepage distance at the radially inner (bottom) portion of the field coils and the radially outer (top) portion of the field coils. The sub-slot covers provide additional insulation and creepage distance between the radially inner portion of the field coils and the rotor body.
Various shapes and configurations of rotor slot insulation are known. For example, U.S. Pat. No. 4,162,340 to Fuchs discloses rotor slot insulation having an L-shaped profile or a U-shaped profile of laminated and compressed substances. A partial area of the rotor slot insulation such as the shorter leg (i.e., foot) of an L-shaped profile or the base of a U-shaped profile is thickened. U.S. Pat. No. 5,065,064 to Kaminski discloses rotor slot insulation which eliminates the need for sub-slot covers through the use of rotor slot armors having Z-shaped profiles. As yet another example, U.S. Pat. No. 4,560,896 to Vogt et al. discloses a composite slot armor and sub-slot cover having a one-piece, integrally molded construction.
There are two manufacturing processes which are commonly used to produce rotor slot armor for large turbine-generators. One process entails an autoclave process which involves producing a laminated composite armor comprising aramid paper (e.g., Nomexâ), polyimide film (e.g., Kaptonâ), woven glass fabric, and epoxy. The other process utilizes a compression-step-molding process using similar materials. U.S. Pat. No. 3,974,314 to Fuchs, U.S. Pat. No. 4,473,765 to Butman, Jr. et al., and U.S. Pat. No. 4,582,749 to Boulter et al. disclose further examples of various materials used to produce rotor slot armor.
In addition to these two processes, an extrusion die system comprising a first die for extruding a material to form a first layer and a second die for applying one capping layer onto the first layer is known. For example, a die system for extruding a low temperature polymer (i.e., polymer having a low melting temperature (Tg<200Â° C.) onto another low temperature polymer for forming vinyl house siding is known.
The current processes for manufacturing rotor slot armor are laborious. Also, expensive materials and equipment are needed. The current processes are difficult to control and often produce high scrap rates and/or inconsistent product quality. The current processes also impose limitations on the design of the cross-sectional shapes of armor that may be produced. Furthermore, composite laminate slot armor produced using these manufacturing processes may not possess the mechanical properties that make it easy and/or effective to assemble into the rotor body. Also, interfaces of the adjacent laminate layers of the slot armor may form weak joints which may have a low dielectric breakage strength and a low mechanical strength. The slot armor formed by laminated layers may thus break rather easily.
Accordingly, there remains a need for a system and process for manufacturing rotor slot armor which is relatively inexpensive and which can accommodate a large variety of shapes and thicknesses. There also remains a need for a rotor slot armor material which exhibits long life and other beneficial mechanical properties such as high flexural modulus, flexual strength, angular strength, electrical creepage, and dielectric strength as well as other properties such as reduced crack propagation, low moisture absorption and improved solvent resistance for reducing electrical failures due to chemical contamination.